Every year volunteers of the fish conservation group, Trout Unlimited, donate 500, 000 hours to clean up polluted rivers, restore fish habitat and fish populations.

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Every year those volunteers donate 500, 000 hours to clean up polluted rivers, restore fish habitat and fish populations.

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That could mean that fish distributions are being affected, as fish avoid places polluted by man-made noise.

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For example, freshwater systems polluted with excess agricultural fertiliser will suffocate with algae, killing off fish and making water unfit for human consumption.

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It safeguards more than 1, 000 miles of our rivers, protects watersheds and cleans up polluted groundwater, defends our oceans and Great Lakes, and will revitalize our fisheries, returning fish to rivers that have not seen them in decades.

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In the Winnebago system, the fish were helped by state laws and a period in the 1970s and 1980s when the polluted waters were so murky that they were hard to catch, except during the spawning season.

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Polluted water increased health risks and harmed the ecology of the river, resulting in the deaths of large numbers of fish in "extreme cases", he told MPs.

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